I need to refresh my towels. They all smell.

Use a cup of vinegar in the wash. It will remove soap residue. It's also good to change the type (manufacturer) of laundry detergent every few months to eliminate build up. Hang them outside in the sun helps too. Using a fabric softener creates a build up in the towels also. The fabric softener works by creating the build up to make it softer. That's why they don't dry as well.

Use lysol in your washer, just a few tablespoons, you won't be able to smell it after they go through the dryer. It provides antibacterial agents

When you wash them add a 1/2 cup baking soda during rinse cycle to deodorize. I also use the second rinse option on my washer.

Wash them with a little vodka. Takes out smelliness

Add 1 cup of ammonia to wash only as frequently as needed

Use only about half of recommended laundry soap every time to prevent buildup

Add 1/2 cup of white vinegar to rinse every time

You should wash the towels in hot water every now and then to keep them odor free. Of course if the towels are white you can use bleach and hot water. I also like to use Borax about twice a month added in the wash cycle this helps wash out soap build up that may be causing the odor. Using less soap and no fabric softener which both have waxy ingredients that stick to clothes, will also help.

Use Lysol laundry disinfectant. I've been using it ever since it became available. I wouldn't be without it.